NEUTRON MEASUREMENTS ON ZFX

The NRL ZFX Facility is being used to form dense Z pinches from single fibers composed of cryogenically frozen deuterium (D2) or deuterated polyethylene (CD2). Fiber diameters range from 40 to 125 μm. Maximum current through all these pinches has been about 1 MA with a rise time of 670 ns. Total neutron yields per shot are measured with a pair of rhodium foil activation counters mounted coaxial and perpendicular to the fiber axis. In order to include the effects of external scattering and absorption these detectors are calibrated in situ using a 252Cf neutron source at the pinch location. Total neutron yields have also been determined using bubble detector dosimeters. This is believed to be the first application of these detectors on a pulsed plasma source. Neutron energy spectroscopy and production time are determined with either a pair of scintillator/photomultiplier detectors located at two different perpendicular distances from the pinch axis or a single microchannel plate photomultiplier (μcp-pmt) detector. Both x-ray shielding and neutron flux collimation are required on these detectors. Typically the detected neutrons (up to 2×109 per shot) were emitted in two to four distinct but overlapping 150-200 ns wide bursts starting 300-400 ns after the current initiation.